Mobile ComputingMidterm Review

D. All of the above

Portable devices and wireless links let people use computing services while moving.

B. GPRS

GPRS adds packet-switched data service to GSM. TCP is a transport protocol and FDMA is a channel-sharing method.

C. Wireless-enabled device

The question describes two wireless-enabled endpoints. A wireless endpoint can also reach wired hosts through network infrastructure.

D. All of the mentioned

GSM is commonly divided into the Base Station Subsystem, Network Switching Subsystem, and Operations Support Subsystem.

D. Base Station Subsystem

In GSM the BSS is the radio-access subsystem, comprising BTSs and their BSC. In Wi-Fi, BSS means Basic Service Set.

A. Network Switching Subsystem

The GSM core subsystem switches calls and manages subscriber information and mobility.

A. Operational Support Subsystem

The OSS supports network operations and maintenance, including monitoring and configuration.

A. Network Switching Subsystem

The NSS contains the MSC and subscriber databases, making it the core for switching and mobility management.

A. Home Location Register

The HLR is the home network’s subscriber database.

A. BSC

A Base Station Controller supervises multiple Base Transceiver Stations and their radio resources.

A. Base Station Controller

The controller coordinates BTSs, assigns radio channels, and handles local handovers.

B. TDMA

Time Division Multiple Access assigns different users time slots within a recurring frame.

A. Connecting a mobile to the PSTN

The MSC switches calls toward the PSTN. The BTS provides the mobile’s radio connection.

A. Mobile Switching Centre

The MSC switches calls and participates in mobility and service control.

D. General Packet Radio Service

GPRS is the packet-data extension for GSM and is often called 2.5G.

B. GSM

GSM is the underlying 2G standard. HSCSD and GPRS are data enhancements built on top of it.

B. GSM

GSM itself is a 2G standard, while GPRS is its 2.5G packet-data enhancement. FDMA is a generic access method rather than a 2.5G standard, so C also fits a literal reading.

The PDF marks A (GPRS). The item is ambiguous and that marking conflicts with the usual classification of GPRS as a 2.5G enhancement using GSM time slots.

A. IEEE 802.11

IEEE 802.11 defines the MAC and physical-layer variants used by Wi-Fi.

A. Hexagon

Regular hexagons tile the plane and approximate a roughly radial footprint.

A. To minimize interference

Using different nearby frequencies reduces co-channel interference in a conventional reuse plan.

C. A small geographical area

A cell is the geographic coverage region served by a base station or sector.

A. A mobile enters a different cell while in conversation

The active call needs its radio connection transferred. An idle device generally performs cell reselection.

D. Ethernet

Ethernet is typically a wired LAN technology. The other options refer to cellular standards, methods, or generations.

D. IEEE 802.11b

802.11b was the High Rate extension for the 2.4 GHz band and reached a nominal 11 Mbps.

B. Analog

First-generation cellular networks carried voice over analog radio channels.

A. Digital

2G digitized voice and enabled services such as SMS.

D. All of the above

Packet data lets applications exchange email, load web pages, and transfer files.

A. 2.5G

The packet-data upgrade is conventionally called 2.5G because it builds on 2G GSM.

A. TDMA

TDMA is the second step that creates time slots. GSM combines FDMA for carrier separation with TDMA within each carrier.

B. FDMA

FDMA gives users separate frequency channels. TDMA separates them in time, while CDMA uses codes.

A. Cell

The overall service region is partitioned into coverage areas called cells.

D. All of the above

The MSC switches calls, the VLR holds local subscriber records, and the HLR maintains home subscriber profiles.

D. All of the above

The MSC communicates with peer switches and can reach the PSTN through an appropriate gateway. Choices B and C are redundant in the scan.

D. All of the above

The MSC participates in registration, MSC–BSS signaling, and call or handover coordination. Detailed radio resource management is primarily handled by the BSS.

A. Home Location Register

The HLR maintains subscription information and tracks the current serving network location.

A. MSC

A VLR is often co-located or integrated with an MSC to serve subscribers in its area.

B. GPRS

GPRS provides the cellular packet service. TCP can operate over it as a transport protocol.

B. IEEE 802.11

IEEE 802.11 defines wireless LANs. IEEE 802.15 addresses wireless personal area networks.

D. IEEE 802.15

IEEE 802.15.1 adapted early Bluetooth specifications. The Bluetooth SIG maintains the Bluetooth specifications today.

D. All of the above

A shared radio medium is susceptible to noise and interference, and contention can reduce usable throughput.

C. FDMA

FDMA splits spectrum into narrower channels. TDMA separates access by time, and CDMA distinguishes users through spreading codes.

The PDF marks D. C is the technically precise answer when bandwidth means a slice of frequency spectrum.

A. Assign different channel groups

A conventional frequency-reuse plan separates nearby cells by assigning different channel groups. Power control and antenna design can also help manage interference.

A. WAP gateway

A classic WAP gateway translates between the WAP protocol stack and web protocols.

D. All of the mentioned

Security and performance management are OSS functions. The EIR checks equipment identities and is usually described as a core network database.

The PDF marks D using a broader operations-and-security grouping. A and B are the direct OSS functions.

C. All of the mentioned

The SGSN serves the mobile and the GGSN provides the gateway to external packet networks.

B. SGSN

The SGSN serves the mobile’s packet-domain attachment and works with subscriber and authentication databases.

A. GGSN

The GGSN uses the active PDP context and serving SGSN address to tunnel incoming packets. The SGSN also maintains local mobility and delivery context.

D. All of the mentioned

The NSS includes the MSC for switching and the HLR and VLR for subscriber and location records.

B. False

An inter-cell handoff needs suitable target radio resources to carry the active connection.

A. Handoff

Handoff moves an active connection to a suitable target channel or cell.

C. 2.4 GHz

802.11b uses the 2.4 GHz ISM band.

B. 11 Mbps

The 802.11b amendment supports a maximum PHY rate of 11 Mbps. Application throughput is lower.

D. 2.4 and 5 GHz

802.11n supports operation in both bands, although individual products may support only one.

B. 802.11ax

The 802.11ax peak assumes a wide channel, high-order modulation, and multiple spatial streams.

B. CSMA/CA

Stations sense the channel and use randomized backoff to reduce collisions.

B. Service Set Identifier

The SSID is the identifier typically displayed as the Wi-Fi network name.

A. Connect wireless devices to a wired LAN

An AP connects associated stations to a distribution system, commonly an Ethernet LAN.

B. Ad hoc mode

An independent basic service set is the classic 802.11 ad hoc topology.

B. Wireless collisions are hard to detect

A transmitting radio cannot reliably listen for a collision at the remote receiver while it is transmitting.

B. Mitigate the hidden-terminal problem

Nearby stations that hear either reservation frame can defer, reducing hidden-station collisions.

C. ACK

For an ordinary acknowledged unicast exchange, the receiver replies with an ACK.

B. Two stations cannot hear each other but interfere at the receiver

Both stations may sense an idle channel and transmit simultaneously to a receiver within range of both.

D. Data

RTS, CTS, and ACK coordinate access or reception. A data frame belongs to its own frame class.

D. 4

The general format allows up to four addresses. Many common frames use fewer.

B. Receiver address

Address 1 identifies the immediate over-the-air receiver, which may be an AP rather than the final destination.

C. Transmitter address

When present, Address 2 identifies the immediate transmitter of the frame.

A. BSSID or final destination address

Address 3 can be the BSSID or destination depending on the direction and frame type. In data frames from the distribution system, it can carry the original source address.

A. When the station requests them

A sleeping station wakes, learns of buffered traffic through an indication such as the TIM, and retrieves it using the applicable power-save mechanism.

B. Accessing computation, data, and services as location or network attachment changes

Mobile computing supports access while the user or device changes location or network attachment.

B. Mobile hardware, mobile software, and mobile communication

Devices run mobile software and communicate over wireless or mobile networks.

B. Bandwidth

In networking usage, bandwidth refers to link capacity in bits per second. In radio engineering it can also mean spectral width in hertz.

C. Time required for a message to reach its destination

Latency is delay. One-way latency measures how long delivery takes from sender to receiver.

C. Distance and obstacles

Increasing distance raises path loss, while obstructions can absorb, reflect, or diffract signals.

B. Changing location or network attachment while services remain available

Mobility concerns continuity of access across movement or changes in connectivity.

A. User mobility

The person can access the same service and task from different devices. Preserving the active task can also illustrate session mobility.

A. Device mobility

The same physical handset changes its network attachment as it moves.

B. Prevent repeated switching between two networks

A margin requires the target to be sufficiently better before switching, reducing ping-pong from small signal fluctuations.

B. Network mobility

A whole local network moves and keeps an external connection through its mobile router.

B. An ongoing application session across devices or networks

Session continuity keeps application state available across a change of device or connection.

B. Provide wireless connectivity and mobility support

The access network supplies the radio link and connects the device to the rest of the network.

A. Mobile traffic to Internet and application services

Gateways and APIs connect mobile clients with backend services and external networks.

B. Ad hoc or device-to-device network

Devices form direct links without relying on a centrally managed AP for the exchange.

A. 1G

Analog cellular systems such as AMPS are examples of first-generation service.

B. Digital voice and SMS

2G standardized digital cellular voice and brought text messaging to mass-market phones.

C. 3G

3G substantially improved mobile data speeds and made browsing and other Internet applications more practical.

B. All-IP packet-based architecture

LTE uses packet switching with the Evolved Packet Core. Voice can be carried over IP with VoLTE.

A. The same person signs in on two fixed desktops

The user changes terminals while both terminals stay fixed.

B. User mobility

The same user can reach their files from multiple locations and devices.

B. The same device moves between locations or network attachment points

The device remains the same as its location or point of attachment changes.

B. A smartphone moves from one Wi-Fi AP to another

The same phone reconnects through a different radio access point.

B. Handoff

Handoff transfers an active connection to a new radio resource or point of attachment.

A. Device mobility

The same device moves through different coverage areas and keeps network access.

B. It decreases

At fixed propagation speed, wavelength equals speed divided by frequency, so the two are inversely proportional.

A. Friis equation

In the far field under free-space conditions, Pᵣ = PₜGₜGᵣ(λ/4πd)².

A. Reflection

Part of the incident wave can bounce from a surface and reach the receiver on a reflected path.

B. Diffraction

Diffraction lets part of a wave reach a region that is shadowed from the direct path.

B. Multiple copies arrive with different delays and phases

Copies can combine constructively or destructively. Destructive combination causes a drop in received signal strength.

A. Different frequency bands

Each user occupies a separate frequency channel within the allocated spectrum.

B. TDMA

TDMA shares a channel by giving users different intervals within a frame.

C. CDMA

CDMA lets users share time and spectrum while a receiver distinguishes signals by their codes.

B. OFDMA

OFDMA assigns groups of orthogonal subcarriers and time resources to downlink users.

B. Uplink and downlink use separate frequency bands

FDD uses paired frequencies so uplink and downlink can operate simultaneously.

B. TDD

TDD divides time on a shared frequency channel between uplink and downlink.

C. 45 MHz

Corresponding downlink channels are 45 MHz above the uplink. For example, 890 MHz pairs with 935 MHz.

B. Reuse frequencies and increase capacity

The same spectrum can be reused at suitably separated sites, supporting more simultaneous traffic.

B. They tile a plane without gaps or overlaps

Hexagons form a regular grid while approximating a circular coverage region.

C. 2.6R²

With R measured from the center to a vertex, the hexagon consists of six equilateral triangles of side R. Its area is (3√3/2)R².

B. 2.6 km²

Substitute R = 1 km into (3√3/2)R² to obtain about 2.598 km².

B. Terrain, buildings, and antenna patterns affect propagation

Coverage depends on path loss, obstructions, antenna direction, and local interference.

B. Reusing a frequency group in sufficiently separated cells

Reusing spectrum at a suitable separation adds capacity while limiting co-channel interference.

C. N = i² + ij + j²

The grid axes are 60° apart, so the squared displacement includes the cross term ij.

C. 7

N = 2² + 2×1 + 1² = 7.

C. 7

7 is obtained with i = 2 and j = 1 in N = i² + ij + j².

B. D/R

D is the center-to-center distance between the nearest co-channel cells, and R is the cell radius.

C. Q = √(3N)

Neighboring hexagon centers are √3R apart. The reuse shift adds a factor √N, so D = R√(3N) and Q = √(3N).

The PDF marks B. C is the standard result for this hexagonal model.

D. Four times as many

Area scales as R². Halving the radius quarters each cell’s area.

D. Decrease to 1/16

To keep the same received power at the new edge, scale transmit power by (1/2)⁴ = 1/16.

B. Greater interference and higher battery consumption

Higher power increases energy use and can raise interference at other receivers.

C. Mobile equipment and SIM

Mobile equipment supplies the handset and radio. The SIM represents the subscription and holds authentication material.

A. BTS

The Base Transceiver Station terminates the Um radio interface.

B. Control several BTSs and manage radio resources

The BSC supervises BTSs, allocates radio resources, and coordinates handovers within its scope.

C. MSC

The Mobile Switching Centre switches calls and coordinates mobility and services with other network elements.

B. IMSI

The International Mobile Subscriber Identity identifies the subscription and is stored on the SIM.

C. IMEI

The International Mobile Equipment Identity identifies the device itself.

B. Avoid repeatedly transmitting the permanent IMSI

A locally assigned temporary identity reduces exposure of the permanent subscriber identity.

A. The subscriber’s dialable phone number

The MSISDN is the public telephone number people dial to reach the subscription.

B. Route an incoming call to the serving MSC

The Mobile Station Roaming Number is temporarily allocated for routing an incoming call to the current serving switch.

B. The HLR stores permanent subscriber information and the VLR holds temporary serving-area information

The HLR keeps the master profile and serving-location pointer. The VLR caches the local data needed to serve the subscriber.

A. BSC

Radio resource allocation across BTSs under its control is a BSC responsibility.

B. Maintain lists of device IMEIs

The EIR classifies equipment identities so the network can check whether devices may use service.

A. The network may prevent it from accessing services

The equipment check can bar the physical handset even if someone inserts a different SIM.

B. IMSI

The IMSI combines the Mobile Country Code, Mobile Network Code, and Mobile Subscription Identification Number.

A. LAI

The Location Area Identity appends a Location Area Code to the country and network codes.

A. Entering an area broadcasting a different LAI

An idle device compares the broadcast location area with its registered area and updates when the area changes.

B. The network must page many cells for an incoming call

The network may know the location area without knowing the exact cell, so it pages across that area.

A. More frequent location updates

Mobiles cross area boundaries more often, adding location-update signaling.

B. Maintain an active connection as the mobile moves

The connection transfers to a suitable channel or cell before the old link becomes unusable.

A. Handover

Handover and handoff both describe transferring an active radio connection.

B. Changing the channel or time slot within the same cell

The serving cell stays the same, while the radio resource changes, often to improve link quality.

A. BSC

The BSC manages local radio resources and can coordinate a new channel within the cell.

A. Intra-BSC handover

Both radio endpoints are under the same controller.

B. Inter-BSC handover

The BSC changes while the serving MSC stays the same.

B. MSC

The common MSC coordinates the transfer between its source and target BSCs.

C. Inter-MSC handover

The serving switch changes, so the two MSCs coordinate the active call transfer.

B. The network, using mobile and BTS measurements

The mobile assists with measurements. Network-side control, usually by the BSC or MSC depending on scope, makes the decision.

A. Neighboring-cell signal levels

Measurements of neighboring signals help the network choose a suitable target.

A. Weak serving-cell signal

A weak or poor-quality link can prompt the network to move the active connection to a better radio resource.

A. Avoid unnecessary repeated handovers

The margin makes small or short-lived differences between cells insufficient to trigger a switch.

A. A mobile repeatedly switches between two cells

At the cell boundary, fluctuating signals can make the preferred cell alternate repeatedly.

A. The call drops before the target link is established

The serving link may fail before the mobile can move to the target.

A. Unnecessary handovers

An early switch can waste radio and signaling resources and may lead to another handover soon afterward.

B. Mobile-assisted, network-controlled handover

The mobile reports measurements and the network selects and prepares the target.

A. An available traffic channel

The target needs a radio resource to carry the existing call.

B. After the mobile switches successfully to the target channel

The source resource is cleared after successful target access is confirmed.

A. Use services outside their home network’s normal service area

A visited network can serve the subscriber, subject to authorization and any required roaming agreement.

B. HLR

The HLR is the authoritative home record for subscription identity and services.

A. VLR

The visited VLR caches subscriber data and stores current local registration information.

A. Location registration

Registration tells the visited network that the subscriber is present and establishes serving-area state.

A. Subscriber profile and authentication information

The visited network needs service permissions and authentication material to serve the visiting user.

A. To know where to obtain incoming-call routing information

For an incoming call, the home network can query the serving side for a temporary routing number.

A. Cancellation of the old VLR record

The old local record can be cleared once the home network knows the new serving VLR.

A. Protect the permanent IMSI over the radio

The temporary local alias reduces how often the permanent subscriber identity appears on the radio interface.

A. Roaming enables service in a visited area or network, while handover transfers an active radio connection

Roaming concerns where a subscription is served. Handover concerns continuity of an active link.

B. Wireless uses a shared broadcast medium

Wireless transmissions travel through shared spectrum and can be heard by multiple nearby receivers.

A. Absolute power referenced to 1 mW

Power in dBm is 10 log₁₀(P / 1 mW).

C. 20 dBm

10 log₁₀(100) = 20 dBm.

A. Twice the power

A power ratio of 10^(3/10) is approximately 2.

A. The transmitter selects a more robust, lower-rate MCS

Rate adaptation may select simpler modulation or stronger coding to preserve reliable reception.

A. A signal reaches the receiver via several reflected paths

Reflections create multiple routes to the receiver. Scattering and diffraction can also produce additional paths.

A. It uses distinguishable propagation paths for spatial streams

A suitable multipath channel lets antenna arrays distinguish simultaneous spatial streams and increase throughput.

B. Two stations cannot hear each other but send to the same receiver

Each sender can believe the medium is idle even though their transmissions overlap at the shared receiver.

C. 802.11n

802.11n introduced high-throughput operation using multiple spatial streams and optional 40 MHz channels.

C. Wi-Fi 6

Wi-Fi 6 is based on 802.11ax. OFDMA divides the channel among users, and 1024-QAM can increase data rate when signal quality permits.

A. Schedule station wake periods to save energy

An AP and station can coordinate wake times so the station spends more time asleep.

A. Basic Service Set

An infrastructure BSS is an AP and its associated stations. In GSM, the same acronym means Base Station Subsystem.

A. One AP and its associated stations

The AP is the center of the BSS and serves its associated stations.

B. IBSS

An Independent Basic Service Set is the classic ad hoc topology.

A. Several connected BSSs

A distribution system connects the BSSs so they can provide a single extended service.

A. Connect access points and their BSSs

The distribution system forwards traffic between BSSs and can connect them to other networks.

B. The AP radio interface’s MAC address

The BSSID identifies the specific BSS. An AP advertising multiple BSSs can use distinct virtual MAC addresses.

B. Access point

A typical AP bridges traffic between its wireless BSS and wired Ethernet distribution network.

A. Fewer independent channels and more contention

Wider channels consume more spectrum, which reduces independent channel choices and can increase overlap.

A. 2.4 GHz

Under comparable conditions, the lower frequency typically experiences less propagation loss and penetrates many obstacles better.

B. Listens for Beacon frames

The station listens on channels for periodic AP advertisements.

C. Probe Request and Probe Response

A station can solicit information immediately with a Probe Request, and nearby APs can answer with Probe Responses.

B. Active scanning

Active scanning can solicit responses without waiting for the next beacon. Some channels or operating modes restrict probing.

B. Discover, authenticate, associate, secure, configure IP

The exam sequence uses initial 802.11 authentication and association, followed by security setup and IP configuration. Authentication details vary by security mode.

B. Association ID

The AID identifies the station within the BSS and can be used in traffic indications for power saving.

B. PTK

The Pairwise Transient Key contains a temporal key for unicast protection and is specific to the AP–station pair.

C. GTK

The Group Temporal Key lets authorized stations decrypt group-addressed traffic sent by the AP.

B. ANonce

The authenticator nonce is the AP’s fresh contribution to deriving session keys.

A. SNonce and MIC

The station sends its nonce and a Message Integrity Code, allowing the AP to verify key possession.

C. The four-way handshake never transmits it

The handshake derives fresh transient keys and demonstrates possession of the already established Pairwise Master Key.

B. DHCP

DHCP leases an address and can deliver routing, subnet, and resolver options.

A. It keeps its IP address

The link-layer point of attachment changes while the station remains in the same IP subnet.

A. A Wi-Fi radio cannot reliably detect collisions while transmitting

A sender’s own signal can overpower incoming signals, and an interference event may only be visible at the receiver.

C. It freezes

The counter resumes after the channel is idle for the required interval.

B. SIFS

The Short Interframe Space is shorter than the usual contention interval, so immediate responses get priority.

A. Reduce hidden-terminal collisions

The sender and receiver announce the reserved airtime. Stations that hear the exchange can defer.

C. Immediate radio receiver

The receiver address identifies who should receive the current radio hop. It can differ from the final destination.

A. The station’s source and transmitter address

For this direction, the station is both source and transmitter. Address 1 is the AP receiver and Address 3 is the destination.

A. Fast power control

Uplink power control keeps a nearby strong mobile from overwhelming weaker signals at the base station.

A. True

The user can switch devices and retain access, while device mobility follows the same hardware across locations or attachment points.

GPRS adds packet-switched data to GSM. It shares radio time slots among users as traffic arrives, while the existing GSM circuit-switched domain continues to handle traditional voice calls.

1. Radio access. The mobile station sends packets over the Um air interface to the BTS. The BSS uses a Packet Control Unit (PCU) to manage packet radio resources and sends packet traffic to the SGSN over Gb.
2. Serving node. The Serving GPRS Support Node (SGSN) handles packet-domain attachment, authentication coordination, mobility and routing-area updates, and delivery between the radio network and the packet core.
3. Gateway node. The Gateway GPRS Support Node (GGSN) connects to an external packet data network over Gi. It maintains session routing state and tunnels packets to and from the serving SGSN with GTP over Gn within an operator network or Gp across operator networks.
4. Subscriber data. The HLR holds the subscriber’s GPRS service profile. The SGSN consults it during registration, and authentication data comes from the home network’s authentication functions.
5. Packet session. After GPRS attach, the mobile activates a PDP context, usually specifying an APN. The SGSN selects a GGSN, the nodes establish session state and tunnel endpoints, and the mobile can send and receive IP packets using its PDP address.

The Home Location Register (HLR) keeps a subscriber’s home-network record. The Visitor Location Register (VLR) stores the working copy and local registration state needed to serve that subscriber in the current area.

1. HLR. Holds the permanent IMSI, dialable MSISDN, subscribed services and restrictions, and a pointer to the current serving VLR or other serving node.
2. VLR. Typically associated with an MSC. Stores a temporary copy of relevant subscriber data, the current location area and local identity such as the TMSI.
3. Location update. When the subscriber enters a new VLR area, the new VLR registers with the HLR and receives the subscriber data. The HLR updates its serving pointer and can cancel the old VLR’s record.
4. Incoming call. The home side uses the HLR to locate the serving MSC/VLR, which can supply an MSRN so the call reaches the right serving switch. The switch then pages the mobile in its registered location area.

A handoff transfers an active call or data connection to a different radio channel, cell, or access point so service can continue when the mobile moves or the current link degrades.

1. Measure and decide. In GSM the handset reports serving and neighboring signal measurements, and the network uses these and its own observations to decide when and where to switch.
2. Prepare and transfer. The network reserves a target channel and commands the handset to move. After successful access on the target, it releases the old channel.
3. Balance the timing. A late transfer can drop the call. An early transfer can waste resources. A margin or hysteresis reduces repeated switching between two cells.
4. Scope. The transfer can change channels inside one cell, cross cells under the same BSC, or involve different BSCs or MSCs. Idle cell reselection is a separate procedure.

A GSM network consists of the Mobile Station, the Base Station Subsystem (BSS), the Network Switching Subsystem (NSS), and the Operations Support Subsystem (OSS).

1. Mobile Station (MS). The handset provides the radio and has an IMEI. Its SIM identifies the subscription by IMSI and stores authentication credentials.
2. Base Station Subsystem (BSS). The BTS sends and receives radio signals over Um. The BSC supervises several BTSs, manages radio resources, and controls local handovers. Abis connects BTS and BSC. The A interface connects the BSS to the MSC.
3. Network Switching Subsystem (NSS). The MSC switches calls and coordinates mobility. A gateway MSC routes calls between GSM and other networks. The HLR stores home subscriber records, the VLR stores local records, the AuC provides authentication material, and the EIR checks equipment identities.
4. Operations Support Subsystem (OSS). The operations and maintenance functions monitor performance, manage faults and configuration, and support network maintenance.
5. Call path. For a traditional outgoing voice call, traffic travels from the mobile through BTS and BSC to the MSC, then to its destination through the appropriate switching or gateway network.