Principles of Voice & Data Lesson 5: Analog and Digital Signaling Bellevue Community College Bob Young, Instructor Signaling Categories • Supervision • Addressing • Alerting Let's look at each of these three categories in more detail... Signaling Categories: Supervision • Detects changes to the line –On hook –Off hook –Call transfer –et cetera Signaling Categories: Addressing • Responsible for routing functions – Passes analog or digital routing information to the correct location to establish the connection – What are some analog routing signals? – What are some digital routing signals? Signaling Categories: Alerting • Signals intended for the user – often audible – ring – busy – call waiting – caller ID (inaudible) – et cetera In-Band & Out-of-Band Signaling • In-band signaling shares the same circuit or path as the voice or data • Out-of-band signaling uses a separate path In-Band Signaling • Also called "Channel Associated Signaling," or CAS In-Band Signaling • Standard for POTS lines • Standard for T1 circuits • Several inherent problems: –slow –susceptible to line noise –security issues Out-of-Band Signaling • Also called "Common Channel Signaling," or CCS Out-of-Band Signaling • Standard between Central Offices • Standard for ISDN • Several advantages: – faster – more reliable – more secure E & M Signaling • E & M Signaling is (was) used between Central Offices on trunks • It is (was) also used to connect DID trunks to PBX's E & M Signaling To prevent glare on E & M trunks: Use wink-start signaling! Wink-Start Signaling • A momentary change in line status sent as an acknowledgement. – Momentary loop current ("off-hook") – Momentary battery reversal – Momentary ground Glare • "Glare" is the condition that occurs when both ends of the same trunk are seized by two different switches for two different calls. 2-Wire E&M Voice Voice Voice Voice E-Lead E-Lead M-Lead M-Lead 4-Wire E&M TX Voice TX Voice RX Voice RX Voice RX Voice RX Voice TX Voice TX Voice E-Lead E-Lead M-Lead M-Lead E&M Signaling Types Signal E Lead E Lead M Lead M Lead OffType On-Hook Off-Hook On-Hook Hook I Open Ground Ground Battery II Open Ground Open Battery III Open Ground Ground Loop Current IV Open Ground Open Ground V Open Ground Open Ground SSDC5 Open Ground Open Ground Ground Start Signaling Like E & M Signaling, • Ground Start Signaling is (was) used between Central Offices on trunks • It is (was) also used to connect DID trunks to PBX's Ground Start Signaling Primary advantage/reason for Ground Start Signaling: Prevents glare! Ground Start Signaling • To initiate a call, a ground is applied to the ring wire momentarily • The far end responds by grounding the tip momentarily • Start loop current, send DTMF or MF T1's and In-Band Signaling • Channelized T1 –24 DS0's –64 kbps channels –Minus 8 kbps for signaling –Leaves 56 kbps per DS0 T1's and In-Band Signaling • Unchannelized T1 –One complete data "pipe" –24 x 64 kbps = 1.536 Mbps T1's and In-Band Signaling • Bit robbing • Superframe (SF) robs 2 bits –A&B • Extended Superframe (ESF) robs 4 bits – A, B, C, & D • Indicate on-hook and off-hook for both ends of the circuit Uses for A & B Bits • Used for supervision in: –Digital E&M circuits –Digital loop start circuits –Digital ground start circuits –Digital OPX circuits ISDN • Integrated Services Digital Network • "I Smell Dollars Now!" • "It Still Does Nothing!" ISDN • All digital, from subscriber premise to Central Office • Uses out-of-band signaling • Also called "common channel signaling (CCS) Channel Structure Bearer Service -- 64 Kbs Data Channel -- 16 Kbs Overhead -- 48 Kbs Service Levels • Basic Rate Interface (BRI) – 2 Bearer Services plus 1 Data Channel – (2B+D) – Linking (Bonding) of Bearer Services • Primary Rate Interface (PRI) – 23 Bearer Services plus 1 Data Channel – (23B+D) – Linking (Bonding) of Bearer Services Let's Do the Math… • 2B+D = (2 x 64) + 16 = 144 Kbs • With overhead: 2B+D+O = (2 x 64) + 16 + 48 = 192 Kbs The Data Channel At the PRI level, a single Data Channel can support multiple "T1's" with 24 Bearer Services each. PRI Bearer Services • For example: • 3 "T1's" 24 + 24 +23 B channels 1 D channel "Parts" and Service • ISUP – Integrated Services User Part • SCCP – Signaling Connection Control Part • TCAP –Transaction Capability H Channels • Whenever ISDN B channels are combined, they are called H Channels ISDN H Channels Channel Name H0 H10 H11 H12 Speed (Kbps) 384 1,472 1,536 1,920 B Channels 6 23 24 30 ISDN in the UK • UK: ISDN 2e equivalent to US BRI –Bearer channels are called echannels –Multiple Subscriber Numbering (MSN) service is used to provide voice and data signaling services ISDN in the UK • ISDN 30 equivalent to US PRI • ISDN 30 (ADS 2) provides up to 30 bearer channels – Not compatible with Europe • ISDN 30 (I.421) provides up to 30 bearer channels – Compatible with Europe ISDN Protocols • I.430 • Q.921 • Q.931 • Q.932 • Let's examine these... ISDN Protocols: I.430 • Defines the reference points between the CO and the terminal equipment (user's equipment) ISDN Protocols: I.430 Reference Points • U Interface: 2 wire connection, terminated by an RJ-11 • S/T Interface: 4 wire connection, terminated by an RJ-45 • Network Termination Equipment (NTE) – Converts U Interface to S/T Interface • Terminal Adaptor: connects multiple devices to the S/T Interface ISDN Protocols: Q.921 • This protocol is specific to ISDN • Also known as LAP-D LAP-D (Q.921) • Stands for, "Link Access Procedure - D Channel" • Part of the Q.921 Protocol • Used to control connections LAP-D (Q.921) • Operates solely in the ISDN D-channel • Provides flow control • Provides data reliability ISDN Protocols: Q.931 • This protocol is used to establish and end sessions (voice or data) in other words, it is for: • Establishing connections • Terminating connections Q.931 Message Types Message Setup Call Proceeding Alerting Name SETUP Description Begins data transmission. Message returned to call CALL PROC originator. Equivalent to "ringback." Sent from call receiver to ALERT caller. A connection between a Terminal Adaptor and a CO CONNECT has been established. Connect Connect Acknowledge CONNECT ment ACK Far-end acknowledgement to a CONNECT message Q.931Session Termination Caller B Caller A Step 1 On hook - send DISCONNECT message Step 2 Receive DISCONNECT message Send RELEASE message Step 3 Send RELEASE COMP message Send RELEASE COMP message ISDN Protocols: Q.932 • Used to modify a call (session) in progress –Transfer a call –Place a call on hold –etc. PISN Private Integrated Services Network Connects standard telco services AND LAN and data services PINX • Private Integrated Services Network Exchange • Also called an Integrated Services PBX • Core element in a PISN PISN Advantages • Multiple vendors can be mixed • Multiple communications protocols • Multiple topologies – star, token ring, etc. • Multiple technologies – Ethernet, wireless, satellite • VPN capabilities on public networks PISN: Two Main Elements • End Nodes – VoIP Phones – Computer Work Stations – Servers • Transport Nodes – PBX – Router PISN Signaling Methods • Digital Private Network Signaling Scheme (DPNSS) – Primarily in the UK – Being replaced by QSIG Private Integrated Services Network Q&C Reference Points Q Reference Point • The Q Reference Point is the LOGICAL interface between the local PINX and the remote PINX. C Reference Point • The C Reference Point is the PHYSICAL interface between the local PINX and the remote PINX. Mapping • Q and C reference points must be mapped to each other • This mapping may be static or dynamic On-Demand/Dynamic Mapping • The connection is established on a per-call (per-session) basis • Generally done with TCP (Transmission Control Protocol) Permanent Mapping • Establishes a continuous connection between the logical Q Reference Point and the physical C Reference Point • Example: a CCS (Common Channel Signaling) data circuit C Reference Point • Physical line testing • Network measuring and monitoring SS7 • • • • Signaling System 7 A kind of common channel signaling The backbone of the PSTN The reason wireless phones can roam – IS-41, now called TIA-41 SS7 and ISDN • • • • • They are not the same thing SS7 is a background protocol ISDN is used by the customer directly Both use common channel signaling ISUP (ISDN User Part) of SS7 allows ISDN to use SS7 for call setup and routing Connecting to the PBX • Automatic Route Selection – Uses a static routing table • Least Cost Routing – Looks at the available options and chooses the least expensive routing option PBX Trunks • AC15A: long distance, diverse power sources • AC15B: four-wire trunk • AC15C: OPX trunk • AC15D: for international trunks PBX Architecture • • • • CPU Operating System Line and Trunk Interface Cards Power Supply CTI • Computer Telephony Integration – The voice network and the data network are starting to become one and the same network The unPBX A PC functioning as a PBX Special Feature: API Application Programming Interface ACD • Automatic Call Distribution –The ability to route calls to the next available operator, or sales rep, etc. Why Packet-Switched Voice and Data? • More "bulletproof" than circuitswitched • Can be routed across various media - cable, fiber, copper, satellite... • Greater versatility and functionality • More efficient use of the media REN • Ringer Equivalency Number • Add up all the REN's that are connected to the same circuit • The number shouldn't be greater than 5. The End • Have a great day! White Template White Template Blue Template