CTA IP Networking & Telecommunications Protocols 2 — Questions and Answers
Question 1: In telecommunications, what is a 'trunk' in the context of traditional telephony?
- A single analog phone line for residential use
- A high-capacity communication link that carries multiple voice circuits between switching centers or between a PBX and the PSTN (Correct answer)
- The physical cable connecting a phone handset to its base
- A dedicated leased line between two enterprise sites
Correct answer: A high-capacity communication link that carries multiple voice circuits between switching centers or between a PBX and the PSTN
A telephone trunk aggregates multiple voice channels between switching points (e.g., central offices or PBX to CO), enabling efficient shared transport of many simultaneous calls.
Question 2: What is the significance of RFC 1918 address space in enterprise telecommunications?
- It defines the public IP address ranges assigned to ISPs
- It designates private IP address ranges (10.x.x.x, 172.16–31.x.x, 192.168.x.x) that are not routable on the public internet (Correct answer)
- It specifies IPv6 transition mechanisms
- It defines multicast address ranges for IPTV
Correct answer: It designates private IP address ranges (10.x.x.x, 172.16–31.x.x, 192.168.x.x) that are not routable on the public internet
RFC 1918 defines three private IP ranges that organizations use internally; these addresses must be NATed to a public IP when accessing the internet.
Question 3: What is the difference between UDP and TCP in the context of VoIP transport?
- TCP provides lower latency and is preferred for VoIP; UDP introduces too much overhead
- UDP is preferred for VoIP because it has lower overhead and no retransmission delays; TCP retransmits lost packets, which causes unacceptable voice delay (Correct answer)
- Both protocols perform identically for voice applications
- UDP is only used for signaling; TCP carries all voice media
Correct answer: UDP is preferred for VoIP because it has lower overhead and no retransmission delays; TCP retransmits lost packets, which causes unacceptable voice delay
VoIP uses UDP via RTP because retransmitting late or lost packets would cause voice to sound worse than simply concealing a lost packet; TCP's retransmissions add unacceptable jitter.
Question 4: What does the term 'AS number' (ASN) refer to in internet routing?
- The number of active sessions on a router
- A unique identifier assigned to an autonomous system for use in BGP routing between organizations (Correct answer)
- The administrative distance value of a routing protocol
- The queue depth in a carrier's traffic management system
Correct answer: A unique identifier assigned to an autonomous system for use in BGP routing between organizations
An ASN (Autonomous System Number) uniquely identifies a network or collection of networks under a single administrative domain that uses BGP to exchange routing information with other ASes.
Question 5: What is 'jitter' in VoIP networks and how does it affect call quality?
- The total one-way delay of a voice packet; high jitter reduces call setup speed
- Variation in packet arrival times; high jitter causes choppy audio if the jitter buffer is insufficient (Correct answer)
- The packet loss rate in a VoIP session; affects codec efficiency
- The echo caused by acoustic coupling at the handset
Correct answer: Variation in packet arrival times; high jitter causes choppy audio if the jitter buffer is insufficient
Jitter is the variability in inter-packet arrival times; when jitter exceeds the jitter buffer depth, packets arrive out of order or too late, resulting in choppy voice audio.
Question 6: In Ethernet networking, what is the function of Spanning Tree Protocol (STP)?
- To encrypt traffic between switches
- To prevent bridging loops in redundant switch topologies by logically blocking redundant paths (Correct answer)
- To assign VLAN memberships to switch ports
- To aggregate multiple physical links into a single logical link
Correct answer: To prevent bridging loops in redundant switch topologies by logically blocking redundant paths
STP prevents Layer 2 broadcast storms and loops in networks with redundant switch paths by placing ports in blocking state on redundant links.
CTA IP Networking & Telecommunications Protocols 2
In telecommunications, what is a 'trunk' in the context of traditional telephony?