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| GPON vs EPON |
EPON to provide fixed-line and down 1.25Gbps, using 8b / 10b line coding, the actual rate of 1Gbps GPON supports multiple speed grades, can support asymmetric uplink and downlink rate, downstream 2.5Gbps or 1.25Gbps, 1.25Gbps upstream or 622 Mbps, the actual It needs to decide down the line speed, select the corresponding optical modules, optical devices to improve the rate of price ratio.
Split ratio
Tap the number of ONU (clients) than that is a port OLT (central office) with EPON standard defines the split ratio of 1:32. GPON standard defines the following types of 1:32 split ratio; one sixty-four; 1: 128 in fact, technically EPON system can do higher split ratios, such as 1: 64, 1: 128, EPON control protocol It can support more ONU. Split ratio is mainly confine light module performance by and large split ratio will result in a substantial increase in the cost of the optical module; in addition, PON insertion loss of 15~18dB, large branching ratio will reduce the transmission distance; too many users share Bandwidth is also a big shunt expense ratio.
The maximum transmission distance
GPON system can support a maximum physical distance, when the optical branching ratio is 1:16, it should support the maximum physical distance of 20km; when the optical branching ratio is 1:32, it should support the maximum physical distance of 10km.
EPON and GPON same.
QOS (Quality of Service)
EPON Ethernet header in the MAC layer adds 64 bytes of MPCP (multipoint control protocol), MPCP via messages, state machines and timers to control access to P2MP multipoint topology, dynamic bandwidth allocation DBA. Contents covered include ONU sends MPCP allocated slot, ONU automatic discovery and added to the congestion level of this report in order to dynamically allocate bandwidth. MPCP provides basic support for P2MP topologies, but the agreement was not on the priority business of the sorting process, all the business of competing random bandwidth.
GPON will have a more comprehensive DBA, with excellent QoS service capabilities. GPON service bandwidth allocation will be divided into four types, from high to low priority is fixed bandwidth (Fixed), guaranteed bandwidth (Assured), non-guaranteed bandwidth (Non-Assured) and best effort bandwidths (BestEffort). DBA and define the business container (traffic container, T-CONT) as the upstream traffic scheduling unit, each T-CONT by the Alloc-ID logo. Each T-CONT may contain one or more GEM Port-ID. T-CONT is divided into five kinds of business types, different types of T-CONT have different bandwidth allocation to meet the different traffic delay, jitter, Different QoS packet loss ratio requirements. Characteristics of T-CONT Type 1 is fixed bandwidth fixed timeslots fixed bandwidth (Fixed) allocation for delay-sensitive services such as voice services; characteristics of type 2 slot is a fixed bandwidth but uncertain, the corresponding guaranteed bandwidth (Assured) allocated for jitter less demanding fixed-bandwidth services such as video on demand service; type 3 is characterized by minimum guaranteed bandwidth and the ability to dynamically share surplus bandwidth and maximum bandwidth constraints, corresponding to a non-guaranteed bandwidth (Non -Assured) distribution, service assurance requirements adapted to have burst but the larger flow of business, such as downloading services; characteristics of Type 4 is the best effort (BestEffort), no bandwidth guarantee, suitable for less demanding latency and jitter services, such as WEB browsing service; Type 5 is a combination of the type of finish after the allocation guarantees and non-guaranteed bandwidth and best effort needs additional bandwidth allocated.
Operation, maintenance OAM
EPON OAM no undue consideration, simply defines a ONT remote fault indication, loopback and link monitoring. And is optionally supported.
GPON physical layer defines the PLOAM (Physical Layer OAM), high-level definition of the OMCI (ONT Management and Control Interface), performed at multiple levels OAM management. PLOAM for implementing data encryption, stateful inspection, error monitoring, and other functions. OMCI channel protocol used to manage high-level definition of business, including the ONU function parameter sets, T-CONT type and quantity of services, QoS parameters, request to run the event configuration information and performance statistics, automatic notification system to achieve OLT to ONT configuration, fault diagnostic, performance, and security management.
Link layer encapsulation and multi-service support
EPON Ethernet follows a simple data format, but in the Ethernet header adds 64 bytes of MPCP multipoint control protocol to achieve bandwidth allocation EPON system bandwidth polled, auto-discovery, ranging work. For data services other than services (such as TDM synchronization services) did not make too much research to support that many EPON manufacturers to develop a number of non-standard products to solve this problem, but not ideal, it is difficult to meet carrier-class QoS requirements.
GPON based entirely new transmission convergence (TC) layer, the sub-layer to complete the adaptation of senior business diversity that defines the ATM encapsulation and GFP encapsulation (Generic Framing Protocol), you can choose either to conduct business package. Given the current ATM application is not universal, so only support a GFP encapsulation GPON.lite equipment came into being, it is removed from the ATM protocol stack to reduce costs.
GFP is a universal link layer procedures applicable to a variety of business, ITU defined as G.7041.GPON GFP in a small number of modifications were made in the head GFP frame introduces Port ID, to support multi-port reuse; also introduced Frag (Fragment) segment of instructions to improve the effective bandwidth of the system and only support for variable length data, the data processing mode does not support block-oriented transparent data processing mode.
GPON has a powerful multi-service carrying capacity. GPON TC layer on nature are synchronized using a standard 8kHz (125μm) fixed length frames, which makes GPON can support end-timing and other quasi-synchronous traffic, in particular, can directly support TDM services, the so-called NativeTDM, GPON TDM services have "natural" support.
Epilogue
EPON and GPON is different, from the superior performance GPON EPON, but EPON has the advantage of time and cost, GPON is catching up, the future of broadband access market substitute who may not be who should be coexistence complementary. For bandwidth and multi-service, QoS and security requirements and high technology as the backbone of ATM customers, GPON will be more suitable. For cost-sensitive, QoS, security, less demanding customer base, EPON become dominant.
GPON maximum splitting ratio of 1: 128, EPON only 1:32;
Support GPON downlink bandwidth is not fixed, up to 2.5G / 1.25G, EPON supports only fixed upstream and downstream bandwidth of 1.25G / 1.25G;
Logic GPON transmission distance up to 60KM, EPON is 20KM.
But the actual effect is concerned, EPON and GPON less, the core part of almost all the same, GPON business a little more comprehensive support it, and now GPON EPON much less than the cost, mainly cost GPON optical modules is too high, Only after extensive use, etc. can drop too down.
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